One commonly used form of electrical fuseholder includes a socket body designed to be mounted on a panel so as to accept insertion of fuses from the front of the panel. The fuse is carried and held in place by a knob which fits into an axially extending cylindrical passageway opening onto the front of the socket body. This cylindrical passageway is interrupted by knob or side terminal-receiving orienting slots which interrupt the continuity of the cylindrical surface, making it practically impossible to form a seal between this surface and the knob. Such a seal could be easily effected by a sealing O-ring carried by the outer end portion of the knob if this surface were a continuous one.
Such a knob commonly has a pair of J-shaped bayonet-type contact fingers which interlock with projections on a side terminal in the socket body when the knob is fully inserted and then rotated in a locking direction. In one side terminal design, shown in U.S. Pat. No. 4,072,385 to Wallner, granted Feb. 7, 1978, the side terminal has a circumferentially curving fuse-retaining spring which is axially stressed when the knob is fully inserted. Removal of the knob is achieved by first pressing axially inward on the knob to separate the interlocked parts, rotating the knob in a direction opposite to the locking direction, and then releasing the pressure thereon, whereupon the retaining spring force ejects the knob from the body. Such a fuseholder assembly permits rapid insertion of the fuse-carrying knob as compared with alternative types wherein screw threads are provided on the knob and socket body; however, the fuse-retaining spring can be deformed by constant or careless insertion of the knob.
A fuseholder shown in U.S. Pat. No. 4,477,139 to Urani, issued Oct. 16, 1984 has a socket body side terminal design which is different from that shown in the abovementioned Wallner patent. While the side terminal of the fuseholder shown in the Urani patent does not have a readily deformable fuse-retaining spring as used in the Wallner fuseholder, the side terminals disclosed in this and the Wallner patent, if made to loose tolerances, would not supply a constant pre-loaded electrical contactmaking force against the mating parts of the knob contact fingers and the socket body side terminal, as does the design of the present invention.
A further common problem is also present in a Wallner fuseholder (U.S. Pat. No. 4,072,385) and the Urani fuseholder when the fuseholder knob is of the type having a screwdriver slot-containing head which, when the knob is finally positioned within the socket body, does not project beyond the outer surface of the fuseholder body (or would not do so in the absence of spring pressure). The knob can be removed by inserting a screwdriver into the slot in the knob head and rotating it into its unlocked position only when spring pressure forces the knob outward to a point where it can be grasped and removed from the fuseholder body. It is not an uncommon experience, however, for an operator to extract a suspect fuse, find that it is blown, and place the knob back in the holder temporarily while he goes off to find a replacement fuse. At this point the customary knob spring pressure bearing on the fuse, which normally will eject the knob in the released orientation thereof as described above, is missing. Thus, upon attempting to remove the knob with the spring in this relaxed condition by rotating the knob with a screwdriver, the user finds that the knob remains depressed within the fuseholder body where he cannot grasp it. A sharply pointed knife or the like is then needed to pry or pull the knob out of the fuseholder body.
A similar situation is also encountered in those cases where the retention spring is carried within a conducting sleeve mounted as an extension of the knob assembly, and wherein the fuse end cap accommodated therein has become so corroded so as to freeze to the sleeve. Under such conditions the spring force cannot act against the fuse to assist in the extraction of the knob.